As for the TV shows, Arrow is great. It's not a popular opinion, but I actually think the first season of it was my favorite, possibly because of it being grittier and more realistic. The dark tone felt less effective when later seasons added more fantastical elements to the show. Also, I wish they would come up with a different seasonal arc to the villain trying to destroy the city.
I loved the first season. The first season finale is easily the show's finest moment, and even looking back I think one of the best hours of TV ever (helping to cement my opinion that this is the best show currently on TV, even if it doesn't always reach those highs anymore). I think the second season was the best because Manu Bennett as Slade was the perfect villain; his murdering of Moira felt both shocking and inevitable at the time it happened, which is quite a feat to pull off; on the whole, Slade's thirst for vengeance was terrifying, and Bennett played the part perfectly. The third season was just too busy (and I echo your opinion that the show loses something the more supernatural it gets, although I think it's still pretty fantastic). It was still good, some of it great, but it didn't reach the levels that were reached in the first two seasons. My biggest criticism of the show as a whole is probably the same as yours; they lean too heavily on the entire city being at risk to hang the season on. I think it might be because that first season finale was so fucking incredible that they keep trying to top themselves, but by now they should probably give it a rest. It did lead to one of my favorite lines in the series - Detective Lance in the season 3 finale saying "City's under attack, must be May" or something to that effect.
The Flash is also great, and its eschewing of darkness in favor of Silver Age wackiness has been to its benefit, although my one big criticism is that the romantic subplots keep repeating the same tired, predictable, and painful-to-watch tropes about how Barry can't tell his love interest that he's the Flash because that'll put her in danger even though she's already been put in danger many times and now his relationship with her is suffering because he has to make excuses and run off at inopportune times, blah blah blah.
My biggest problem with the first season was that it took Iris so long to catch on. Or was she told? I can't remember exactly. At any rate, she's a reporter. There was a point where it seemed like everybody
but Iris knew that Barry was the Flash, which kind of just makes her look stupid (of course the exact same criticism can be leveled at Laurel on
Arrow... who's a
lawyer; but really the less said about Laurel's character the better). My other criticism of the show is that some of the time travel elements just don't make sense if you stop to think about them. But it's goofy fun, the TV equivalent of a popcorn movie, so I'm willing to let some of its more glaring flaws slide. Mark Hamill playing The Trickster, basically using his Joker voice from the Batman animated series, was such a hoot.
Constantine I watched when I heard that Matt Ryan was going to guest-star in an episode of Arrow, apparently linking their continuities together. I'm not sure if that really did end up making all the events of that show canon within the Arrowverse/Flarrowverse/whatever, or if it was just Ryan's take on the character. Probably the latter, but I wouldn't blame the CW too much for that, as Ryan's performance was easily the best part of Constantine, which was in all other respects just okay.
I still have to watch
Constantine. I saw the pilot and I guess it just didn't impress me much, because even though I've been a fan of the comics for a long time I just never made it a point to watch it or get caught up on it.
I haven't seen Lucifer at all, but frankly, that show just looks terrible.
I watched the pilot. The guy playing Lucifer (Tom Ellis) seems to be having a lot of fun with it. The fact that it's basically a police procedural featuring Satan in the main role feels like a bad joke. I'd like to think they'll break out of that mold and go for something deeper but I don't have much faith in that happening. I never read Mike Carey's comic but I always loved Neil Gaiman's take on the character in
Sandman. I enjoyed the show despite the fact that its premise is so dumb, probably because of Tom Ellis' performance more than anything else.
And then there's Gotham, which isn't a bad show so much as it is completely fucking nuts. The people behind this don't seem to have any idea what kind of show this is trying to be, and apparently keep trying to re-invent it entirely every few episodes. Or maybe they all just disagree on what the tone should be. In one episode they'll be trying to keep it grounded and gritty like the Nolan films, in another they'll be wanting to base it on the Burton films, in other episodes it goes for camp so goofy that it feels like a tribute to the 60s show, and then there are some episodes that I can only assume were inspired by the Frank Miller comics the writers were using to snort lines of cocaine.
I know it's a common criticism that
Gotham often feels like it doesn't know what kind of show it wants to be. I don't think its lack of consistency is quite as bad as you make it out to be; even at its campiest there's a strain of darkness that puts it above the level of the old TV show, and on the flip side of the coin, even at their darkest the comics still retain some elements of camp; with a Rogues Gallery that includes characters like The Ventriloquist, The Riddler and even The Joker I think that's inevitable. So I don't mind it having a presence on the show and I think it's at least consistent with the comics.
Sometimes the writing is just awful. That whole Jerome subplot was silly and cliched to the point that they were making it so obvious that he was meant to be the Joker that I saw it coming from a mile away that he wasn't going to end up being the Joker. I hate to say "This is how I would have done it..." but hell, this is how I would have done it: I think it would have been interesting if they had introduced a series of characters who each in their own way share traits of the Joker, so that we never really know which one it ends up being (it would have been a nice tribute to the multiple-choice nature of his origin in the comics). But they fucked that up when they made it
so obvious that he was Joker, and then fucked it up worse when they killed that goofy motherfucker off, and the show was still the better for the latter, because he was terrible.
I guess it's mostly the performances that keep me going back, particularly Robin Taylor as Penguin, Donal Logue as Harvey Bullock, and Sean Pertwee as Alfred. The rest of the cast is fine for the most part (and I will never get tired of seeing Morena Baccarin, even if her character is a bit thin), but I
really can't stand the kid that plays Bruce. I don't know; maybe it's just too understated to the point of being boring. But somehow one of the most interesting and complex characters in comics becomes trite and one-note in that performance; too much the mask that is Bruce and not enough the actual character that is Batman, if you follow. I also don't miss Fish Mooney.